Sorting by Surfing: particles separate by riding acoustic waves

Collaborators across the University of Augsburg, Harvard University, and the University of Glasgow create a fluorescence-activated cell sorter relying on acoustofluidics to guide particles to their final location.

Traditional fluorescence-activated cell and droplet sorting (FACS, FADS) machines are expensive and require considerable time for analysis as well as maintenance (i.e., rinsing and cleaning of tubing to prepare for RNase-free processing). Cheap and disposable microfluidic devices can alleviate the expense and maintenance required, but still lag in particle sorting speed because they depend on fluidic, dielectric, and magnetic actuation to direct particles after fluorescence interrogation.

Lothar Schmid, David Weitz, and Thomas Franke overcame these issues by using traveling surface acoustic waves (SAWs) to drive particles into select channels based on readout of a fluorescent signal. The group oscillated PDMS structures from below by embedded interdigitated transducers to achieve focused acoustic radiation forces which gently moved droplets and cells via acoustic streaming.

The group was able to achieve sorting independent of cell size and compressibility on the order of 3000 particles/second into multiple outlet channels. This fast separation of particles given fluorescence signal readout enables efficient sorting of populations which vary widely in shape and volume. Further, the particles did not have to be first encapsulated into drops. This simplification avoids biohazard aerosol formation, provides higher signal to noise on the fluorescent signal interrogation, and streamlines the separation process. The group demonstrated gentle sorting of melanoma cells in a single fluid based on metabolic activity and membrane integrity. It will be exciting to see how acoustic streaming can further be used to direct particles to aid rare cell separations and cell isolations from complex samples.

You can download the full article for free* until the 24th October 2014:

Sorting drops and cells with acoustics: acoustic microfluidic fluorescence-activated cell sorter
Lothar Schmid, David A. Weitz, and Thomas Franke. Lab Chip, 2014, 14, 3710-3718.
DOI: 10.1039/C4LC00588K

*Access is free through a registered RSC account – click here to register

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